DC Generator

10 KW AC generators are pretty common. High current diodes are also easy to come by.

AC to DC using a single or three phase input along with a reverse connected diode to catch the pulse when the coil is disconnected.

Too easy?

Earle Rich Mont Vernon, NH

Someone might have abstract ideas about doing this by rectifying an AC generator, or a similar scheme. But 10 KW is a lot of power and it isn't so simple to just hook up a few parts and have it work for long. Does this thing really use that much ooomph? Where does all the heat go?

45 amps is easy and the parts can be had for very little money. It's done in many welding machines everyday. 600 Volts piv should be fine with a reverse diode for the inductive load.

But I do agree with your comment on that amount of power. Doesn't seem right.

Too easy?...I guess not if you know what you are doing.... 240v DC single phase I assume....don't know the current needed, not sure how to connect a reverse diode and what it would be connected to.... Ken.

Don't know any details other than the original post. Have no idea what kind of current a junkyard magnet would draw. I personally am wondering if he could simply run a dc generator from the motor in the crane from an extra drive pulley or driveshaft someplace. Also don't know what is meant by "going bad" - whether it's the generator portion or the engine is finally wearing out.... I got all this "second hand" as the fella that asked evidently knows the junkyard guy, and thought I may have an idea as to where he could find this generator. Ken.

As I understand it, he (the junkyard guy) claims one of the welding machines won't work as the output is not stable enough.... Ken.

Richard

40 amps at 240VDC may be about right for a big magnet. I've fixed my buddy's magnet several times. It runs from a BIG engine driven welder. It draws over 80 amps at 70 VDC and it isnt a very big magnet. I never thought about how warm that magnet gets. I'll sure feel it next time I see it working. I'm not skilled at making rectifiers but, I'm confidant that even I could build an adequate rectifier for this magnet since all the switching devices are already there for the controls. I was considering suggesting that the guy who is looking for the DC source for that magnet, might be able to save some $$ by finding a military surplus 400 Hz 3 phase 208 VAC power source, since they are much cheaper than 60 Hz.

Jerry

I was not suggesting use of a welder, only that the diodes are in the range of what is required. The best approach would be a three phase generator, maybe something military at 400 Hz. It would be easy to go from 220/3ph/400 to Dc.

tm

Gosh - with this one - you can have coffee also!

$7535.00

GENERATORS G11 INGERSOLL-RAND GENERATOR ID: G11 Model Power Watts Max - 11000 Power VA Max (.8 pf) - 13750 Motor starting power(watts) - 3660 Rated power rating(watts) - 9900 Noise Level(dBa at 7 M) - 73 Enclosure - Enclosed

Engine Engine Brand - Mitsubishi Engine Model - S3L2SD Displacement(cm^3)/Type - 1318/OHV Rated Horsepower/RPM - 17/1800 Standard Starting System - electric start Automatic Idle Control - No Spin On Oil Filter - Yes Spark Arrest Muffler - No Fuel/Capacity(US Gallons) Diesel/11.4 Running Time Full Load(hours) - 12.4 Running Time 75% Load(hours) - 15.6 Running Time Half Load(hours) - 18.9 Gauged Fuel Cap - yes

Generator Output Voltages - 120/240 Circuit Breaker Protection - Yes Outlets - (1) 120v 15a duplex Outlets - (1) 125 V - 30 A Outlets - (1) 125/250 V - 30 A Overload Protection - Yes Number of Poles - 4

Package Length (in/cm) - 66/169 Width (in/cm) - 30/77 Height (in/cm) - 47/119 Dry Weight (lbs/kg) - 1177/534 Wet Weight (lbs/kg) - 1265/574 Protective Shutdowns - Oil PSI + water Temp. Lifting eye - Yes Electric Start with Battery & Cables -Yes Hourmeter - Included Something like this one - Rent Lease until the one there gets fixed.

Mabye buy.

Martin

If you use a FWB, you have two diode drops to take care of the flyback pulse. :)

Tim

-- "I've got more trophies than Wayne Gretsky and the Pope combined!" - Homer Simpson Website @

Martin, Don't know if 30A would be enough.... also don't know if the outputs are "cumulative" to total current capabilities of the generator, ie, 15+30+30 for a total or would this just be 30A max? Ken.

It would be worth looking at the existing generator's controls. I wouldn't be surprised if the magnet is hard wired to the output and the magnet turned on and off by controlling the generator's field.

Ned Simmons

A reverse diode is needed to absorb the inductive overswing when the supply to the coil is interrupted. In the absence of this diode the overswing could reach hundreds or possibly thousands of volts and cause severe arcing at the breaker contacts.The diode should be rated for at least the nominal coil voltage and current. The cathode ( +ve end) of the diode should be wired to directly to the end of the coil that is supplied from supply positive. The diode anode (-ve end) should be wired to the coil negative.

If it can be avoided, it is a bad idea to switch the DC input to the coil. It is much better to feed the coil from a full wave rectified AC supply and switch on the AC side as this is much kinder to the contactor. If the full wave rectifier is permanently wired directly to the coil it also behaves as a reverse diode and the separate diode can be omitted.

Jim

Back to the original poster.....

I don't know how much power you want to make. If you want to make from

500 to 1600 watts of Sine wave AC, forego all "build your own from scratch" ideas and look up "redi-Line" on Ebay.

These are "motor generators", designed to take DC voltage from a car battery 12-36 volts), turn a motor, which in the end drives a generator that puts out Pure sine wave (Clean) power.

These are the precurser to newer electronic "inverters". Though not as "efficient" as newer electronic units (of which you likely do not care

- running Steam and all), this should work Great! These can be had on the used market for far less than the Electronic types (you couldn't use the electronic types for what you are doing anyhow !)

Your mission would be to simply dissassemble the device (you pick the power level you want - I would advice the 1600 watt cause you will likely have the power to turn it) - and expose the motor shaft of the unit, and drive the generator via your Steam engine (3600 rpm is the recommended at full load).

Cool Eh ? Run the microwave via steam power !

I want to see pictures when you are done !

Chris L

On 22 Jun 2004 14:02:04 -0700, snipped-for-privacy@lakefield.net (Chris L) vaguely proposed a theory ......and in reply I say!:

remove ns from my header address to reply via email

Who wanted 10000 W of DC

Your original post asked for a DC generator. Most of the responses you've gotten recommend AC generators with rectifiers. AC generators will be a *LOT* easier to find than DC generators.

I thought I'd mention that this will work fine. A big electromagnet like that will have so much inductance that the current will be essentially DC even if the applied voltage is rectified AC. At 240 volts and 10KW, the avg (DC) current is about 41.6 amps, while the AC ripple current from rectified single-phase AC will probably be well under 1 amp. The difference between this and "pure" DC excitation would not be noticable.

The original post question betrays too much ignorance of what is going on.

10 kW is just to much heat to dissipate on any kind of duty cycle. He may be trying to duplicate a poorly cobbled prior repair or design.

Besides, that many amps into that big an inductor has gotta produce one wollop of a surge when you switch it off. Saying you can absorb that with a reversed diode is like saying you can brake a big diesel engine to a dead stop by putting your hand on the flywheel. I suspect part of the reason for the DC generator is that you can clutch out the prime mover, and the generator becomes a motor to slowly dissipate the stored energy in the inductor.

It's always dangerous to accuse someone of ignorance.

A little research on the web shows that a 10KW/240VDC magnet is actually a small one. Here's a company that sells used round lifting magnets:

Here's the specifications on the biggest one I could find:

That's about 46KW. I guess there must be a way for the heat to dissipate.

I have an old Audel book with a chapter on lifting magnets. It describes the controllers and how the high induced voltage is handled. There's no mention of current or voltage ratings, but the relative size of the controller components and connections would indicate something in the 50-100 amp range.

The Audel book does not speak of any use of the prime mover to control the current, just a controller with contactors and resistors.

True. But he did say as much, which is why he asked for advice.

I'll confess I have no experience with these things.

Still, 46 kW in an 80-inch disk that has to stay cool enough to maintain

240 V insulation doesn't seem like it could have much of a duty cycle. That's about one toaster per square foot of surface area.